Talking of USA, it is one country that significantly increased its post-independence size through purchase of land from Russia, France, Mexico, Denmark etc. It must have made the most profitable land deal in history when it purchased Alaska from Russia at a little over 7 million dollars in 1867, which comes to about $10 per sq. mile (2 cents per acre). Just imagine that Alaska accounts for 20% of total oil production in USA, not to speak of the huge reserves of natural gas, and mineral resources like coal, gold, zinc etc. and you will appreciate the magnitude of the bargain!